Recovery of asphaltic-type petroleum from a subterranean reservoir



United States Patent 3,275,076 RECOVERY OF ASPHALTIC-TYPE PETROLEUM FROM A SUBTERRANEAN RESERVOIR Lorld G. Sharp, Irving, Tex., assignor to Mobil Oil Corporation, a corporation of New York No Drawing. Filed Jan. 13, 1964, Ser. No. 337,134 12 Claims. (Cl. 166-11) This invention rel-ates to the recovery of petroleum from a subterranean reservoir and relates more particularly to the recovery of the petroleum by methods involving displacement of the petroleum from the reservoir by injection of a displacing fluid into the reservoir.

Petroleum is ordinarily recovered from a subterranean reservoir or formation in which it is present by reason of the natural enery within the reservoir forcing the petroleum therefrom into a well leading from the surface of the earth to the reservoir. The reservoir energy, in most instances, is insuflicient to effect recovery of all of the petroleum in the reservoir. Thus, the amount of petroleum that may be recovered from a reservoir through utilization of the natural energy may not be greater than about one-third of the petroleum originally in place in the reservoir. To improve the extent of recovery of petroleum from a reservoir, various methods involving the application of extrinsic energy to the reservoir are employed.

Among the recovery methods involving application of extrinsic energy to the reservoir are those wherein a displacing fluid is employed. In these methods, the displacing fluid is injected into the reservoir through an injection Well leading thereto from the surface of the earth. The displacing fluid enters the reservoir and forces the petroleum through the reservoir into the direction of a production wellleading thereto from the surface of the earth. The petroleum enters the production well and is thereafter removed from the well.

Recove1'y methods involving the use of a displacing fluid which is miscible with the petroleum in the reservoir are particularly effective from the standpoint of the amount of petroleum recovered. In these methods, the miscible displacing fluid dissolves the petroleum and carries the dissolved petroleum along with it as it moves through the reservoir. Thus, the miscible displacing fluid displaces substantially entirely all of the petroleum from that portion of the reservoir through which it passes. Displacing fluids miscible with the petroleum that are most frequently used are liquefied petroleum gas (LPG) and carbon dioxide.

The miscible displacing fluid can be followed into the reservoir with a driving fluid which is relatively inexpensive compared to the displacing fluid. The driving fluid may or may not be miscible with the displacing fluid. Where the driving fluid is miscible with the displacing fluid, the driving fluid displaces substantially entirely all of the displacing fluid from the portion of the reservoir from which the driving fluid displaced the petroleum. The displacing fluid thus is moved into another portion of the reservoir from which it displaces petroleum. As a result, little or none of the displacing fluid remains in the reservoir and high recoveries of petroleum per unit amount of displacing fluid employed are obtained. Where the driving fluid is not miscible with the displacing fluid, the driving fluid does not displace all of the displacing fluid from the portion of the reservoir which it entered. As a result, a portion of the displacing fluid remains in the reservoir and the amount of petroleum recovered does not exceed the amount of displacing fluid employed.

While a miscible displacing fluid is particularly effective from the standpoint of the amount of petroleum displaced from the reservoir, various ditiiculties are encountered- Patented Sept. 27, 1966 Ice from using such fluid. More particularly, where the petroleum in the reservoir is asphaltic, the miscible displacing fluid, upon dissolving the petroleum in the reservoir, effects precipitation of the asphaltic constituents of the petroleum in the form of solid particles in the reservoir. The solid asphaltic constituents precipitated from the petroleum tend to block the interstices of the matrix of the reservoir containing the petroleum and thereby reduce the permeability of the reservoir to the flow of-the displacing fluid and of any driving fluid. Reduction in the permeability of the reservoir at any location therein will increase the pressure required to maintain a. desired rate of flow of the displacing fluid and of any driving fluid into the reservoir. However, since the linear rate of flow of any fluid injected into the reservoir is greatest at the injection well, reduction in the permeability of the reservoir in the vicinity of the injection well increases the pressure required to maintain a desired rate of flow of fluid to a greater extent than at other locations in the reservoir. In aggravated cases, the reduction in permeability in the vicinity of the injection well may be to the extent that flow of the displacing fluid and of any driving fluid cannot be effected by any pressure practically att-ained without fracture of the'matrix of the reservoir.

It is an object of this invention to provide a method for avoiding precipitation of asphaltic constituents from petroleum within a reservoir upon injection into the reservoir of a displacing fluid miscible with the petroleum. It is another object of this invention to decrease the pressure required to maintain a desired rate of flow of a displacing fluid miscible with the petroleum and of any driving fluid into a subterranean formation containing an asphaltic petroleum. These and other objects of the invention will become apparent from the following detailed description.

In accordance with the invention, a subterranean reservoir containing asphaltic petroleum is, prior to injection therein through an injection well of a solvent miscible with the petroleum to displace the petroleum from the reservoir, subjected to the action of an oxidizing fluid under conditions eifecting combustion of petroleum within the reservoir in the vicinity of the injection well.

By the procedure of the invention, reduction in permeability of the reservoir upon introduction therein of the miscible displacing fluid is avoided. By the step of effecting combustion of petroleum Within the reservoir in the vicinity of the injection well, the asphaltic petroleum is removed from the reservoir in the vicinity of the injection well. The combustion step effects thermal decomposition of the petroleum with the format-ion therefrom of light hydrocarbons which migrate comparatively readily through the reservoir under the influence of the injected oxidizing fluid. Further, as a result of the thermal decomposition, the asphaltic constituents of the petroleum form a graded, low viscosity, low asphalt oil which also migrates comparatively easily under the in-' fluence of the injected oxidizing fluid. Additionally, by the thermal decomposition, a coked material can be deposited within the reservoir which, subsequently, with continuation of combustion, is completely burned. Accordingly, the matrix of the reservoir, subsequent to the combustion step, is free of the original asphaltic petroleum or of its thermal decomposition products. With subsequent injection of the miscible displacing fluid, there is no precipitation of asphaltic constituents in the reservoir in the vicinity of the injection well. Thus, by the procedure of the invention, the reservoir in the vicinity of the injection well is brought to a maximum permeability and the pressure required to maintain a desired rate of flow of displacing fluid and of any driving fluid is at a minimum.

3 In the practice of the invention, .it is preferred that, as a preliminary step, permeability of the reservoir be established to the flow of the oxidizing fluid to be employed in the combustion step. By thus establishing permeability, assurance can be had that the oxidizing fluid can be injected into the formation at a rate sufliciently high to maintain combustion. Permeability to the oxidizing fluid is established merely by injecting the oxidizing fluid under pressure into the reservoir through the injection well and continuing injection until a practicable rate of flow of oxidizing fluid into the reservoir at a practicable pressure of injection is attained.

The oxidizing fluid employed for the combustion step is preferably air. However, other oxidizing fluids may be employed, if desired. Foriexample, air containing an inert gaseous constituent such as carbon dioxide or added nitrogen to reduce the oxygen content may be employed. As a source of carbon dioxide for reducing the oxygen content of the air, flue gas may be employed. Further, if desired, the oxygen concentration of the air may be increased by adding oxygen to the air. Moreover, the oxidizing fluid may have added thereto various types of materials affecting the combustion step. Thus, for example, hydrocarbon fluid may be added to the oxidizing fluid to assist combustion. Further, for example, catalytic agents to retard or to accelerate combustion may also be added to the oxidizing fluid.

Following establishment of permeability of the reservoir to the oxidizing fluid, combustion is effected within the reservoir. For this purpose,, any of the conventional methods for initiating combustion may be employed. For example, a heater may be positioned within the injection well adjacent to the formation and operated to bring the temperature within the reservoir in the vicinity of the well to the ignition temperature of the petroleum therein. The heater may be any type of heater, for example, the heater may be a gas fired or an electrical heater, heretofore employed for initiating combustion within a reservoir. With attainmentof the ignition temperature, and supply of the oxidizing fluid to the reservoir, combustion of the petroleum within the formation occurs. Combustion may also be initiated employing chemical means. Thus, for example, a suitable material, such as yellow phosphorus, may be deposited within the reservoir and, with supply of oxidizing fluid, combustion will be initiated. Further, for example, with various typesof petroleum, combustion will occur spontaneously upon passage of the oxidizing fluid through the reservoir. Where the reservoir contains such petroleum, combustion can be initiated merely by injecting the oxidizing fluid into the reservoir. Where the petroleum ,within the formation is such that it will not attain ignition temperature solely with passage of the oxidizing fluid, petroleum capable of spontaneous ignition may be placed in the reservoir in the vicinity of the injection well and therafter the oxidizing fluid injected into the reservoir.

' Following initiation of combustion within the reservoir, I

combustion is continued for. such time that the asphaltic petroleum is removed from the reservoir for a suitable distance from the injection well. With the linear rate of flow of any fluid injected into the reservoir being greatest at the injection well, the pressure drop of the oxidizing fluid passed through the reservoir will. become progressively less per unit distance of linear flow with distance from the injection well. Accordingly, combustion is continued until the petroleum is removed from the reservoir for a distance from the injection well that any reduction in permeability caused by precipitation of asphaltic constituents in the petroleum by solution in the miscible displacing fluid subsequently injected into the reservoir will not be of significance from the standpoint of obtaining a desired rate of flow of displacing fluid or of 4 r petroleumhas been removed from the reservoirfor a distance of at leastabout 30 feet from the center of the injection well. Combustion may be continued,'of course, until the petroleum has been removed from the reservoir for a greater distance. I Thus, for example, combustion may be continued until the petroleum has been removed from the reservoir for a distance of 60 feet or more from the center of the injection well. Y

Subsequent to removal of the petroleum from the reservoir for the desired distance from the injection well, the injection of the oxidizing fluid, and thus the combustion, is discontinued. v

Subsequent to discontinuation of combustion, the mis-.

cible displacement fluid is injected into the1reservoirthrough the injection well. The miscible displacement fluid employed will be liquefied petroleum gas or carbon dioxide. Liquefied petroleum gas consists essentially of low molecular weight hydrocarbons which, under the conditions of pressure in'which they are used, are in a liquid state. Carbon dioxide,under. normal conditions of temperature andpressure, is a gas. However, under the.

conditions of pressure in which the carbon dioxide is used,

it remains in the liquid phase or is sufl'lciently soluble in the petroleum to approximate the displacement efliciency. of the liquid phase.

The amount of the miscible displacing fluid injected into the reservoir may be conventionally employed- Ordinarily, the miscible displacing fluid is sufliciently expensive that less than the total pore volume of the reservoir isemployed. Thus, ordinarily, the amount of miscible'displacing fluid employed is only a fraction of the total pore volume of the reservoir between the injection well and the production .well or wells through which the Satisfactory results have been;

through which the fluid passes, the miscible displacingfluid can be followed by a driving fluid. Any of the conventionally employed driving fluids may be used, Thus, natural gas may be employed as the driving fluid. Employing liquefied petroleumgas. as the displacing fluid, natural gas as the driving fluid .will be miscible with the liquefied petroleum, gas where the natural gas is ,maintained upon injection at a pressure of at least 1000 pounds per square inch. Water may also be used as the driving fluid.

While the step of efiecting combustion within the reservoir prior to injection ofthe miscible displacing fluid is primarily of utility from the standpoint of avoiding reductionin permeability of the formation, it has other. advantages. For example, subsequent to the combustionj' step, the portion of the reservoir through which combustion has been etfected will be saturated with gas. Further, thehighly permeable zones within the reservoir beyond the point where combustion has been efliected will also be saturated to a large extent with gas. On the other hand, the less permeable zones within thereservoir be yond the point where combustion has been effected will be saturated to a lesser extent with gas or will be free of gas. As is known, the permeability of the reservoir to a liquid is inversely proportional to the extent of gas satu- 1 ration. Thus, the high gas saturation of the highly permeable zones tends to block themovement of liquid in these zones.

the highly permeable zones, is minimized and a greater sweep vefliciency by the displacement procedure is obtained.

In a particular embodiment of the invention, wateris. injected into the, reservoir subsequent to discontinuation Accordingly, bypassing of themiscible displacing fluid, and driving fluid where employed, through of the combustion step and prior to injection of the miscible displacing fluid. The portion of the reservoir in which combustion took place will be at a high temperature. The water has a high specific heat, and the water injected into the reservoir will remove heat from the portion of thereservoi-r in which the combustion took place and pass it into the adjoining portion of the reservoir in the direction of the production well. Thus, by injection of the water, the petroleum in the portion of the reservoir beyond the point where combustion was effected becomes heated and its viscosity consequently becomes reduced. As a result, the movement of the petroleum in the direction of the production well is facilitated.

Injection of water into the reservoir subsequent to the combustion step provides an additional advantage where the miscible displacing fluid employed is liquefied petroleum gas and the driving fluid is water. With injection of the water into the reservoir, the matrix of the reservoir tends to become water-wet. Upon subsequent passage of the liquefied petroleum gas through the waterwet reservoir, a lesser amount of liquefied petroleum gas will remain within the reservoir because of the greater difficulty of displacement of water than of gas by the liquefied petroleum gas. Thus, by the step of injecting water into the reservoir, a lesser amount of the liquefied petroleum gas is left in the reservoir and consequently a greater amount of liquefied petroleum gas is available for displacement of petroleum.

Further advantages accrue from the injection of water into the reservoir subsequent to the combustion step. One of these arises from the fact that the water passes preferentially into the zones containing the hydrocarbons having a lower mobility produced by the combustion step and into the zones of higher permeability. By so doing, the permeability of these zones to the subsequent liquefied petroleum gas injected into the reservoir is reduced. Accordingly, bypassing of the miscible displacing fluid through these zones with premature breakthrough at the production well is minimized. Another of the advantages arises from the fact that the water effects displacement of petroleum from the reservoir beyond the portion in which combustion had been carried out. As a result, the volume of the reservoir containing asphaltic petroleum is decreased. Thus, the volume of reservoir around the injection well from which asphaltic petroleum which would precipitate asphalt upon contact with the miscible displacing fluid has been removed is increased.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

Iclaim:

1. A method for the recovery of asphaltic type petroleum from a subterranean reservoir wherein a fluid capable of miscibly displacing said petroleum is injected into said reservoir through a first well and moved through said reservoir to a second well and injection of said fluid etfects precipitation of asphaltic constituents from said petroleum and thereby reduces the permeability of said reservoir from the standpoint of obtaining a desired rate of flow into said reservoir of said fluid and said fluid bypasses through highly permeable zones in said reservoir, comprising the steps of:

(a) effecting combustion of said petroleum in said reservoir in the presence of an oxidizing fluid adjacent to a first well penetrating said reservoir to remove said petroleum from said reservoir from a distance from said first well such that reduction in permeability of said reservoir by precipitation of asphaltic constituents will not be of significance from the standpoint of obtaining a desired rate of flow of said fluid and highly permeable zones Within said reservoir beyond said distance trom said first well will be saturated to a large extent with gas whereby permeability of said zones to said fluid is reduced,

(b) discontinuing said combustion of said petroleum,

(c) thereafter injecting into said reservoir through said first well said fluid capable of miscibly displacing said petroleum from said reservoir and displacing said petroleum within said reservoir toward said second well whereby precipitation of asphaltic constituents from said petroleum by said fluid will not occur within said reservoir at a distance from said first well that reduction in permeability of said reservoir by said precipitation will be of significance from the standpoint .of obtaining a desired rate of flow of said fluid and the movement of liquid in said zones having reduced permeability as a result of said gas saturation tends to be blocked whereby bypassing of said fluid is minimized, and

(d) recovering said petroleum from said reservoir through said second well.

2. The method of claim 1 wherein an oxidizing fluid is passed into said reservoir prior to effecting combustion of said petroleum in order toetfect permeability to said fluid in said reservoir.

3. The method of claim 1 wherein said combustion is continued until said petroleum has been removed from said reservoir for a distance of at least 30 feet from the center of said first well.

4. The method of claim 1 wherein said fluid which is miscible with said petroleum is injected into said reservoir in an amount at least as great as 2 percent of the total pore volume of said reservoir between said first well and said second well.

5. The method of claim 1 wherein said fluid which is miscible with said petroleum is liquefied petroleum gas.

6. The method of claim 1 wherein said fluid which is miscible with said petroleum is carbon dioxide.

7. The method of claim 1 wherein said fluid which is miscible with said petroleum is passed through said reservoir in the direction of said second well by injecting a driving fluid into said reservoir through said first well.

8. The method of claim 7 wherein said driving fluid is natural gas.

9. The method of claim 7 wherein said driving fluid is water.

10. The method of claim 1 wherein following step (b) and prior to step (c) water is injected into said reservoir through said first well whereby said water passes preferentially into zones containing hydrocarbons having a lower mobility produced by said combustion in step (a) and into zones of higher permeability whereby bypassing of said fluid is further minimized and the heat contained in said reservoir as a result of said combustion is moved into said reservoir in the direction of said second well to heat said petroleum within said reservoir and thereby reduce its viscosity.

11. The method of claim 1 wherein said fluid capable of miscibly displacing said petroleum is liquefied petroleum gas and, following step (c), water is injected into said reservoir through said first well as a driving fluid.

12. The method of claim 11 wherein following discontinuing of said combustion and prior to said injection of a fluid capable of miscibly displacing said petroleum water is injected into said reservoir through said first well whereby the matrix of said reservoir is wetted with water with consequent reduction in the amount remaining in said reservoir of said subsequently injected liquefied petroleum gas and whereby said water passes preferentially into zones containing hydrocarbons having a lower mobility produced by said combustion step and into zones of higher permeability with the results that bypassing of said fluid is further minimized and said heat contained in said reservoir is moved into said reservoir in the di- 33,036,632 5/1962 Kochet a1. 166.-11 rection of said second well tov heat said pqtroleum therein 3,084,744 4/1963 Dew et a1. ,1669 n r d i v y- 3,093,191 6/1963 Glass ,166-11' 7 3,103,972. 9/1963 Parker ,166-9 References Cted by the Examme' 5 3,121,462 2/1964 Martin-ct a1. 166-43 x UNITED STATES PATENTS 3,174,543 3/1965 Sharp 166 1.1 2,390,770 1 2/1945 Barton e a1. .166-11 3,193,008 7/1965 Moore ',1661'1 2,722,277 11/1955 Crawford .16611 r 2,863,5 10 12/1958 Taderna et a1. 16639 X CHARLES E. OCONNELL, Primary Examiner.

2,901,043 8/1959 Campion et a1. 166-11 10 3,024,841 3/1962 winman S. J. NOYO SAD, Assistant Examiner. 

1. A METHOD FOR THE RECOVERY OF ASPHALTIC TYPE PETROLEUM FROM A SUBTERRANEAN RESERVIOR WHEREIN A FLUID CAPABLE OF MISCIBLY DISPLACING SAID PETROLEUM IS INJECTED INTO SAID RESERVIOR THROUGH A FIRST WELL AND MOVED THROUGH SAID RESERVIOR TO A SECOND WELL AND INJECTION OF SAID FLUID EFFECTS PRECIPITATION OF ASPHALIC CONSTITUENTS FROM SAID PETROLEUM AND THEREBY REDUCES THE PERMEABILITY OF SAID RESERVIOR FROM THE STANDPOINT OF OBTAINING A DESIRED RATE OF FLOW INTO SAID RESERVIOR OF SAID FLUID AND SAID FLUID BYPASSES THROUGH HIGHLY PERMEABLE ZONES IN SAID RESERVIOR, COMPRISING THE STEPS OF: (A) EFFECTING COMBUSTION OF SAID PETROLEUM IN SAID RESERVIOR IN THE PRESENCE OF AN OXIDIZING FLUID ADJACENT TO A FIRST WELL PENETRATING SAID RESERVIOR TO REMOVE SAID PETROLEUM FROM SAID RESERVIOR FROM A DISTANCE FROM SAID FORST WELL SUCH THAT REDUCTION IN PERMEABILITY OF SAID RESERVIOR BY PRECIPITATION OF ASPHALTIC CONSTITUENTS WILL NOT BE OF SIGNIFICANCE FROM THE STANDPOINT OF OBTAINING A DESIRED RATE OF FLOW OF SAID FLUID AND HIGHLY PERMEABLE ZONES WITHIN SAID RESERVIOR BEYOND SAID DISTANCE FROM SAID FIRST WELL WILL BE SATURATED TO A LARGE EXTENT WITH GAS WHEREBY PERMEABILITY OF SAID ZONES TO SAID FLUID IS REDUCED. (B) DISCONTINUING SAID COMBUSTION OF SAID PETROLEUM, (C) THEREAFTER INJECTING INTO SAID RESERVIOR THROUGH SAID FIRST WELL SAID FLUID CAPABLE OF MISCIBLY DISPLACING SAID PETROLEUM FRONT SAID RESERVIOR AND DISPLACING SAID PETROLEUM WITHIN SAID RESERVIOR TOWARD SAID SECOND WELL WHEREBY PRECIPITATION OF ASPHALTIC CONSTITUENTS FROM SAID PETROLUEM BY SAID FLUID WILL NOT OCCUR WITHIN SAID RESERVIOR AT A DISTANCE FROM SAID FIRST WELL THAT REDUCTION IN PERMEABILITY OF SAID RESERVIOR BY SAID PRECIPITATION WILL BE OF SIGNIFICANCE FROM THE STANDPOINT OF OBTAINING A DESIRED RATE OF FLOW OF SAID FLUID AND THE MOVEMENT OF LIQUID IN SAID ZONES HAVING REDUCED PERMEABILITY AS A RESULT OF SAID GAS SATURATION TENDS TO BE BLOCKED WHEREBY BYPASSING OF SAID FLUID IS MINIMIZED, AND (D) RECOVERING SAID PETROLEUM FROM SAID RESERVIOR THROUGH SAID SECOND WELL. 